Everything you need to know about protecting your home and equipment from electrical surges — what causes them, the three types of Surge Protection Device (SPD), the BS 7671 Amendment 2 requirement, and what installation costs.
Free for 7 days · No charge until day 8 · Cancel anytime · Used by 1,000+ UK electricians
Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
1,000+
UK electricians
“Replaced three separate apps with Elec-Mate. Certs, quotes, and scheduling all in one place.”
Daniel Palmer — DP Electrical
A power surge is a sudden, brief increase in voltage above the normal supply level. The UK mains supply is nominally 230 volts (V) alternating current (AC). A surge can momentarily raise this to hundreds or even thousands of volts, lasting anywhere from a fraction of a millisecond to a few milliseconds.
Although brief, these transient over-voltages can cause immediate catastrophic failure of sensitive electronic components, or — more insidiously — degrade them over time through repeated smaller surges that reduce reliability before causing eventual failure. Modern electronics use lower-voltage transistors and integrated circuits with increasingly fine tolerances, making them more vulnerable to surge damage than older equipment.
Every key change in the 2026 amendment on one page. AFDDs, TN-C-S protection, new schedule columns, model forms. Pinned on your van dash.
Power surges have several distinct causes, ranging from large external events to everyday switching within a property.
Surge Protection Devices (SPDs) are classified into three types based on where they are installed in the electrical system and what level of surge energy they are designed to handle. A coordinated system uses all three types together.
Located at the service entrance (at or near the electricity meter, between the meter and the consumer unit). Designed to handle the very high peak currents from direct lightning strikes — typically 25kA or more. Mandatory under BS 7671 where a lightning protection system exists on the building. Uses spark gap technology or a combination of spark gap and MOV.
Installed inside or directly adjacent to the consumer unit (fuse box). Handles the residual surge energy that passes through a Type 1, plus internally generated switching surges. This is the most common SPD installed in domestic properties. Uses Metal Oxide Varistors (MOVs). Required in most new domestic installations under BS 7671 Amendment 2.
The final line of protection, installed in socket outlets, within appliances, or in surge-protected extension leads. Handles only small residual surges not already absorbed by Type 1 and 2 devices. Cannot be used alone as the only protection — it must be used downstream of Type 2 protection to be effective. The surge-protected extension leads sold in consumer electronics shops are Type 3 devices.
The 18th Edition of BS 7671 (the IET Wiring Regulations) was amended by Amendment 2, which became effective from 28 March 2022. This amendment significantly strengthened the requirements for surge protection in UK electrical installations.
Electricians completing new consumer unit installations should familiarise themselves with the Amendment 2 requirements. See our BS 7671 18th Edition guide for a full overview of the Amendment 2 changes.
SPDs protect against transient over-voltages — sudden spikes of short duration. They are not designed to protect against sustained over-voltages (such as a neutral conductor fault that causes one phase to rise to 400V) or against sustained power outages.
16 certificate types, 70+ calculators, RAMS, quoting, invoicing, AI agents, and 46+ training courses — from £6.99/mo.
Start free trial
The cost of SPD installation depends on the type of SPD, the consumer unit configuration, and the electrician's rates in your area.
Not all SPDs are equal. When specifying a Type 2 SPD for a domestic consumer unit, look for the following key parameters.
For qualified electricians, SPD installation has become an increasingly common requirement following the Amendment 2 changes. Understanding the risk assessment methodology and SPD coordination is essential.
BS 7671 Regulation 443.4 requires a risk assessment for every new installation. Document whether the supply is overhead or underground, the lightning protection zone, and the consequences of failure. If the assessment concludes SPD protection is not required, record why — this protects you if the decision is later questioned.
Use the Elec-Mate certificate app to complete the Electrical Installation Certificate (EIC) for new consumer unit installations, including SPD details. Correct documentation is essential for Part P compliance and for your customer's records.
Join 1,000+ UK electricians using Elec-Mate for on-site certificate completion, AI board scanning, and instant PDF export.
Try it free for 7 daysVerified reviews from the UK App Store.
Elec-Mate is my go to app for business and electrical work. It's feature rich without feeling cluttered. A true all in one app for quotes, certs, calculations, RAMS, EICRs, and more. I use it every day without fail, and it makes my workflow much smoother since I'm not jumping between apps anymore. The price-to-feature ratio is excellent. Any issues I've had, the developer responds within the hour and usually fixes them the same day. 100% recommend.
I've used the app and the web based version for a while now and it's well worth the investment. If you're an apprentice or experienced Spark give it a go, you won't be disappointed.
I've been using Elec-Mate for a while now, and honestly, it's one of the best apps I've ever downloaded. Every aspect of it feels thoughtfully designed, from the clean and intuitive interface to the powerful features that make everything so easy to manage. It's clear that a lot of care and attention went into building this app, and it shows in every detail.
Real feedback from real sparks
“Replaced three separate apps with Elec-Mate. Certs, quotes, and scheduling all in one place.”
Daniel Palmer
Sole Trader · DP Electrical
“I've won two contracts this month because I could turn quotes around same-day with the AI cost engineer.”
Nathan Perry
Electrician · NP Electrical Services
“The study centre got me through my AM2. Mock exams and flashcards are brilliant.”
Jake Pizey
3rd Year Apprentice · Apprentice
Complete EICs and EICRs on your phone, including SPD documentation. Join 1,000+ UK electricians. 7-day free trial, cancel anytime.
“Replaced three separate apps with Elec-Mate. Certs, quotes, and scheduling all in one place.”
Daniel Palmer, DP Electrical
From £6.99/mo after trial — less than a coffee a week
We use cookies to improve the app and measure what works. Cookie Policy